FI120682B - Process for recovering hydrochloric acid from an iron chloride solution - Google Patents

Description

A method for recovering hydrochloric acid from an iron chloride solution

FIELD OF THE INVENTION The present invention relates to a process for the recovery of hydrochloric acid from an iron chloride solution by reacting an iron chloride with sulfuric acid to produce an iron sulfate thymonohydrate. More particularly, the present invention relates to such a process wherein the hydrochloric acid is evaporated under reduced pressure and then recovered by condensation.

10

Background of the Invention

In certain processes, such as industrial processes, recovery of hydrochloric acid from a solution containing sulfur chloride is necessary. One such industrial process 15 is the pickling of steel with hydrochloric acid in the treatment of steel. An aqueous waste solution is formed containing ferric chloride and hydrochloric acid. The used pickling solution is considered as hazardous waste. For environmental reasons, for example, hydrochloric acid must be recovered and possibly recycled.

Methods for recovering hydrochloric acid from an iron chloride solution are known in the art. US 5,417,955 discloses a two step process for processing iron (II) chloride from a pickling solution. Iron (II) chloride is first mixed with sulfuric acid to form iron (II) sulfate and HCl. The HCl is transported to an absorption tower where most of the HCl is collected and the residue is returned to the reactor. The iron (II) sulfate is separated from the sulfuric acid. Unreacted sulfuric acid is returned to the reactor and iron (II) sulfate is transported to another reactor where it is reacted with sulfuric acid and air (O 2) T to form iron (III) sulfate. The iron (III) sulfate is removed from the second reactor. Both reactions are carried out at relatively low temperatures under atmospheric pressure. The air treatment used in US 5,417,955 is commonly referred to as the airstrip 30 break.

US 3,635,664 discloses a process for the recovery of hydrochloric acid from hydrochloric acid pickling waste by distillation comprising the step of adding sulfuric acid to the hydrochloric acid waste to convert FeCl 2 into 35 HCl and FeSO 4 in said waste and obtain a mixture containing at least 38% by weight of sulfuric acid; distilling said resulting mixture to evaporate substantially all of the HCl along with water and precipitate the iron (II) sulfate; condensing thus evaporated said HCl and water to recover hydrochloric acid; separating the precipitated iron (II) sulfate from the residual liquid; and recycling the iron (II) sulfate-free residual liquid as a sulfuric acid source. Example 1 illustrates a process in which part of the HCl is removed in an expansion distillation unit and the remainder of the HCl is removed in another distillation apparatus. In another example, the chemicals are mixed in a reactor and HCl is distilled in an evaporation / distillation tower combination.

However, the described methods and device arrangements have some drawbacks. For example, Example 3 of US 3,635,664 illustrates the use of the apparatus shown in Figure 3 wherein HCl is distilled in an evaporation / distillation tower combination. Under the reaction conditions described, solids may precipitate in the system. Since the distillation apparatus has only a weak thermosyphone mix, it may clog.

In addition, the air stripping method described in US 5,417,955 has a pressurized reactor. In such a process, there is always a risk of leakage, in which case the strongly acidified mixture is widely distributed from the reactor. In addition, in known processes, multiple vessels or reactors are necessary, whereby the arrangement of the devices becomes complex, space-consuming and expensive. Also, the high temperatures used in some processes can cause corrosion and require energy.

20

Summary of the Invention

The present invention provides a process for the recovery of hydrochloric acid: from an iron (II) chloride solution, wherein the iron chloride is mixed with sulfuric acid; 25 to obtain a reaction mixture having a sulfuric acid concentration of at least 55% (w / w) to produce hydrochloric acid and ferrous sulfate monohydrate, followed by evaporation and recovery of the hydrochloric acid by condensation to yield hydrochloric acid; the acid is evaporated under reduced pressure to 225 mbar or less and both mixing, evaporation and precipitation of ferrous sulphate monohydrate are carried out in the same single vessel. In one embodiment, the sulfuric acid concentration is about 60% (w / w) or more. At least a portion of the ferrous sulphate monohydrate is separated and recovered. In one embodiment, the iron chloride solution is the pickling solution used.

It was surprisingly found that to recover substantially all hydrochloric acid, only evaporation under reduced pressure was necessary. In addition, mixing of solutions, evaporation of hydrochloric acid, and precipitation of ferrous sulfate monohydrate can be carried out in a 3 mass vessel as the reaction. This has several advantages over the prior art.

One benefit is that the process is simpler and can be performed in a simpler and more compact device, it requires less investment and saves space and time. In addition, it is more reliable.

Another advantage is that the reaction compounds are mixed in said same vessel, for example by utilizing a stream of recycled sulfuric acid or by mechanical agitation.

One advantage is that since low temperatures can be used, the process of the present invention saves energy. Lower temperatures also lead to fewer problems with corrosion.

15

Yet another advantage is that when utilizing low pressure evaporation, the system is safe to use compared to pressurized systems such as air-hanging systems.

BRIEF DESCRIPTION OF THE DRAWINGS% Figure 1 shows a schematic view of one embodiment of apparatus which is' usable in the process of the present invention.

Figure 2 shows a schematic view of another embodiment of apparatus which is' - * usable in the process of the present invention.

Figure 3 shows a schematic view of another embodiment of apparatus useful in the process of the present invention.

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Detailed Description of the Invention

The iron chloride solution which can be used in the process of the present invention contains 2-valent (ferro) iron chloride. At the sulfuric acid levels and 35 temperatures used herein, the major product is iron (II) sulfate monohydrate (FeSCVH 2 O). The reaction with sulfuric acid may be as follows:

FeCl 2 + H 2 SO 4 + H 2 O → FeSO 4 H 2 O + 2 HCl

4

One example of starting material containing iron (II) chloride is the pickling solution used. The used pickling solution is mixed with sulfuric acid to give a reaction mixture having a sulfuric acid concentration of at least 55% (w / w) to produce hydrochloric acid and ferrous sulfate monohydrate, followed by hydrochloric acid evaporation and condensation in aq. mixing, evaporation and precipitation of ferrous sulphate monohydrate are carried out in the same single vessel. At least a portion of the ferrous sulphate monohydrate is separated and recovered and the unreacted sulfuric acid can be recycled.

10

In the process of the present invention, both the reaction and evaporation steps are carried out in the same individual vessel (or reactor, since the terms herein can be used interchangeably). The reacting compounds may also be mixed in said vessel. The term "vessel" as used herein refers to any suitable vessel in which said reaction occurs, such as a reactor or the like. In one embodiment, the unreacted sulfuric acid is recycled and recycled to the reactor at a flow sufficient to cause the reactive solutions to mix in the reactor, for example, 20 to 60 t / h in a vessel of about 3 m 3. In another embodiment, a mixer such as a mechanical mixer is used.

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The pickling solution and sulfuric acid are fed to the vessel in such doses that the concentration of free sulfuric acid should be at least 55% by weight in the reaction mixture in the vessel. Typically, most of the sulfuric acid introduced into the vessel is unreacted sulfuric acid, which is recycled from the iron sulfate monohydrate separation step. The concentration of sulfuric acid in the vessel can be adjusted to the desired concentration by introducing fresh concentrated sulfuric acid into the vessel. It is also essential to remove the used U »:; excess water from the pickling solution during the evaporation step to maintain the sulfuric acid concentration at the desired concentration. Generally, the preferred sulfuric acid concentration is at least about 60% by weight in the reaction mixture in the vessel.

If the concentration is significantly lower, the reaction slows down and the concentration of chloride in the iron sulphate monohydrate product increases. For some uses of iron sulfate monohydrate, such as in animal nutrition, a low chloride concentration is necessary. In addition, chloride-induced corrosion is avoided.

The temperature of the reaction mixture in the vessel may range from 70 to 100 ° C. In one embodiment, a preferred range is 80 to 95 ° C. The heating may be carried out using any suitable heating method known in the art. Examples of heating methods include a heating jacket, a heating coil, and combinations thereof. However, especially in a large-scale process, it is difficult to obtain a sufficiently large heating surface required for heat transfer. In one embodiment, an external heat exchanger is used for heating and the unreacted sulfuric acid is fed through the heat exchanger and recycled to 5 reactors / vessels. Generally, when using a heat exchanger, the recycled unreacted sulfuric acid is heated to about 20 ° C higher than the temperature of the reaction mixture in the vessel.

When evaporating hydrochloric acid and water, the pressure should be low, for example 225 to 10 mbar or less. At higher pressures, the temperature required for evaporation would be too high, for example at about 300 ° C at about 300 ° C. At such high temperatures, corrosion will increase and some materials, such as plastics or the like, may not be resistant. In one embodiment, the pressure is about 110 mbar or less. A smaller heat exchanger may then be used. Also, the corrosion of the device cor-15 is further reduced.

After evaporation, the hydrochloric acid is recovered, for example, by condensation using any suitable capacitor known in the art, such as a plate or tubular capacitor.

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In addition, at least a portion of the ferrous sulfate monohydrate precipitated during the sulfuric acid treatment is clarified, separated and recovered. Clarification is achieved in a vessel where mixing and evaporation take place. In general, coarse iron sulphate crystals precipitate and are easily recovered. Some of the fine 25 flour is flowing with the sulfuric acid in the circulation and can act as nuclei to facilitate further crystallization. Since clarification in the vessel is desired, the vessel may be specifically designed to provide efficient separation of coarse iron sulfate crystals. The sulfuric acid outlets are fed to the top of the vessel where mixing takes place. Clearing occurs in the calmer lower part. The Vir-30 tails can be oriented to provide a circulating motion of the solution, in which case the heavier particles first drive the heavier particles onto the vessel wall, from where they then sink to the bottom.

Also disclosed is a method wherein a mixture containing ferrous sulfate monohydrate 35 and sulfuric acid is directed to a clarification tank in which a portion of the ferrous sulfate monohydrate is depressed. The final liquid, which contains unreacted sulfuric acid and may contain small amounts of ferrous sulfate monohydrate, is fed from the top of the clarification tank to the heat exchanger and recycled back to the reactor as a source of sulfuric acid.

6

The clarified iron sulfate monohydrate is introduced into a separating medium and separated. Another method is disclosed wherein the clarification takes place in a reactor and a sulfuric acid solution containing only a small amount of ferrous sulfate monohydrate is fed to a heat exchanger and recycled to the reactor. In yet another process, a mixture containing ferrous sulfate monohydrate and sulfuric acid is conducted to a clarification tank where a portion of the ferrous sulfate monohydrate is depressed. The clarified iron sulfate monohydrate is introduced into a separating medium and separated. The final liquid, which contains unreacted sulfuric acid and may contain traces of iron sulfate monohydrate, can be recycled from the top 10 of the clarification tank back to the reactor. In this process, an unreacted sulfuric acid solution containing only small amounts of ferrous sulfate monohydrate is also passed from the reactor to the heat exchanger and recycled to the reactor. The process can be a continuous process or a batch process. Various embodiments of the apparatus can be utilized in the process, such as those described below.

15

An example of a device arrangement useful in the process of the invention is shown in Figure 1. Defined as 1, there is a line for feeding an aqueous acidic waste solution containing iron (II) chloride to reactor 15. The reactor may be provided with means for stirring the contents (not shown). The reactor is further provided with line 2 for feeding fresh 20 sulfuric acid from tank 21, line 3 for condenser 20, line 7 for circulating heated unreacted sulfuric acid, line 23 for circulating sulfuric acid from intermediate tank 18 and line 5 connected to clarification tank 16. 8 to a separating means 17, such as a filter or centrifuge. Line 10 is for removing iron (II) sulphate monohydrate from the separating means 17 and line 9 leads to the filtrate intermediate tank 18. Line 6 is connected between the clarification tank and the heat exchanger 19. Line 11 is feeds Line 12 is an outlet for the heat exchanger heating medium. Line 13 is feeds Line 14 is the outlet for condenser cooling medium. Vacuum is maintained in reactor and condenser by vacuum pump 22 through line 24. The condensed aqueous HCl-30 mixture is removed at line 4.

Another example of an arrangement of apparatus useful in the process of the invention is shown in Figure 2. In this apparatus, clarification is already occurring in reactor 15 and no clarification tank is required. Defined by 1, there is a line for feeding an aqueous acidic waste solution containing iron (II) chloride to reactor 15. The reactor may be provided with means for stirring the contents (not shown). The reactor is further provided with line 2 for supplying fresh sulfuric acid from tank 21, line 3 connected to condenser 20, line 7 for recycling unreacted sulfuric acid 7, and line 23 for recycling sulfuric acid from intermediate tank 18. Reactor 15 is directly connected to line 8 for separation means 17 such as filter or centrifuge. Line 10 is iron (II) for removing sulfate monohydrate from the separating means 17 and line 9 leads to the filtrate intermediate tank 18. Line 25 is connected between the reactor 5 and the heat exchanger 19. Line 11 is feeds Line 12 is an outlet for the heat exchanger heating medium. Line 13 is feeds Line 14 is the outlet for condenser cooling medium. Vacuum is maintained in the reactor and condenser by a vacuum pump 22 through line 24. The condensed aqueous HCl mixture is removed at line 4.

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Another example of an arrangement of apparatus useful in the method of the invention is shown in Figure 3. This apparatus is supplied from a clarification tank 16 to reactor 15. Defined by 1 is a line for feeding an aqueous acidic waste solution containing iron (II) chloride to reactor 15. between the switch 19. The reactor may be provided with means for mixing the contents (not shown). The reactor is further provided with line 2 for supplying fresh sulfuric acid from tank 21, line 3 for condenser 20, line 7 for recycling unreacted sulfuric acid, and line 23 for recycling sulfuric acid from intermediate tank 18. Reactor 15 is connected to clarification tank 16 and line 5 is also clarity tank. back to reactor 15 at line 6. The clarification tank 16 is connected at line 8 to a separation means 17 such as a filter or centrifuge. Line 10 is iron (II) for removal of sulfate monohydrate from separation medium 17 and line 9 leads to filtrate intermediate tank 18. Line 25 is connected between reaction tank 15 and heat exchanger 19. Line 11 is feed line 12 is outlet for heat exchanger 7. Line 13 is feeds Line 14 is the outlet for condenser cooling medium Vacuum is maintained in the reactor and condenser by vacuum pump 22 through line 24. The condensed water-HCl mixture is removed by line 4.

30 Pumps can be used in the equipment as needed, for example, on most lines indicated by an arrow in the figures. In some cases, stock feeds can operate under vacuum without pumps, but it is generally preferred to use pumps to maintain a steady feed.

35 The principle of the continuous process shown in Figure 1 is as follows. The used pickling solution is fed through line 1, typically at a flow rate of 0.5 to 3 t / h, for example a flow rate of 1.7 t / h, to reactor 15 where it reacts with sulfuric acid. The sulfuric acid concentration is maintained in the reactor 15 at a desired concentration of at least 55% (w / w) by dispensing fresh sulfuric acid through line 2 at a flow rate of 0.05 to 1 t / h, typically at a flow rate of 0.3 t / h from storage tank 21 and of heated unreacted sulfuric acid (recycled unreacted sulfuric acid) through line 7 at a flow rate of 10 to 100 t / h, typically at a flow rate of 5 t / h to the reactor. The heat required to evaporate the hydrochloric acid is introduced into the reaction mixture using an external heat exchanger 19. The unreacted sulfuric acid is fed to the heat exchanger via line 6 and recycled to the reactor via line 7. Unreacted sulfuric acid is heated to 90-130 ° C, typically to about 110-120 ° C. In this embodiment, the heat exchanger heating medium is vapor, but other heating media may also be used.

The pressure in the reactor 15 is maintained at a desired level, such as 100 to 200 mbar, by a vacuum pump 22. At said pressure, the temperature in the reactor is in the range of 80 to 95 ° C depending on the sulfuric acid concentration of the wood. The hydrochloric acid / water vapor evaporates through line 3 to condenser 20 where it is condensed and fed to a storage tank via line 4. For example, at a flow rate of 1.7 t / h of the pickling solution used, about 1.5119-20% hydrochloric acid is obtained.

Iron (II) sulfate monohydrate crystallizes in a sulfuric acid solution after it has formed in the reaction. The mixture is then continuously fed to a clarification tank 16 through line 5. Most of the iron (II) sulphate monohydrate product is clarified in the clarification tank 16. It can be separated from the main stream 5 using a hydrocyclone, a clarification tank, a centrifuge or any other suitable separation method known in the art. The overflow is led back to the reactor via a heat exchanger and the clarified fraction is fed to the pressure filter through line 8. The final separation of iron (II) sulfate monohydrate from the solution is carried out by filtration, preferably by pressure filtration. Other filtering methods may also be used, such as a belt filter or a drum filter. The iron (II) sulphate monohydrate crystals 30 are removed through line 10. For example, at a flow rate of 1.7 t / h of the pickling solution used, about 0.51 iron sulfate monohydrate is obtained. The filtrate is recycled back to the reactor, preferably via an intermediate tank 18.

Claims (12)

A process for recovering hydrochloric acid from an iron (II) chloride solution, which process comprises mixing ferric chloride with sulfuric acid to provide a reaction mixture having a sulfuric acid concentration of at least 55% (w / w) to produce hydrochloric acid and ferric sulfate monohydrate at 225 mbartai, the aliquots are recovered by condensation, characterized in that both mixing, evaporation and precipitation of ferrous sulphate monohydrate are effected directly in a single vessel. 2. Förfarande enligt patent krav 1, rotation pattern 20, and circus 60% (w / w). Process according to claim 1, characterized in that the sulfuric acid concentration is about 60% (w / w) or more. 3. Förfarande enligt patentkrav 1 eller 2, kangnetecknat av att ätminstone en del ', avsulfatmonohydrat avskiljs frän oreagerande svavelsyra and tervinns. 25 4. Förfarande enligt nägot av de föregäende patentkraven, kännetecknat av att *. :; oreagerande svavelsyra ätervinns tillbaka account reopening. Process according to claim 1 or 2, characterized in that at least a portion of the iron sulphate monohydrate is separated from the unreacted sulfuric acid and recovered. Process according to any one of the preceding claims, characterized in that the unreacted sulfuric acid is recycled to the vessel. 5. Förfarande enligt patentkrav 4, kännetecknat av att blandningen ästadkoms genom att Mata oreagerande svavelsyra tillbaka account retrieval. 30 Process according to Claim 4, characterized in that the mixing is effected by feeding the unreacted sulfuric acid back into the vessel. 6. Förfarande enligt Face to face patent for a patent application, kännetecknat av att blandningen ästadkoms av en blandare. Method according to one of the preceding claims, characterized in that the mixing is effected by means of a mixer. 7. Förfarande enligt face av de föregäende patentkraven, kännetecknat av att 35 ° C, and this temperature is reduced to 70-100 ° C. Process according to any one of the preceding claims, characterized in that the temperature of the reaction mixture in said vessel is in the range of 70-100 ° C. 30 8. Förfarande enligt face av de föregäende patentkraven, kännetecknat av att tempuren av reactionsblandningen i det, at 80-95 ° C. Process according to any one of the preceding claims, characterized in that the temperature of the reaction mixture in said vessel is in the range 80-95 ° C. 9. Förfarande enligt nagot av de föregaende patentkraven, kännetecknat av att min prov tryck and 110 mbar eller mindre. 5 10. Förfarande enligt nagot av de föregaende patentkraven, kännetecknat av att afterchlorideslösning and använt betningslösning. Method according to one of the preceding claims, characterized in that the reduced pressure is less than 110 mbartai. Method according to one of the preceding claims, characterized in that the ferric chloride solution is a pickling solution used. 11. Förfarande enligt nagot av de föregäende patentkraven, kännetecknat av att det so förfarandet utförs som en kontinuerlig process. 10 Process according to any one of the preceding claims, characterized in that said process is carried out as a continuous process. Process according to any one of claims 1 to 10, characterized in that said method 5 is carried out in a batch process. 10 1. Förfarande för ätervinning av saltsyra frän järn (ll) chlorideslösning, i förförfarande - förkloriden blandas med svavelsyra för attfa en reactationsblandning, förfelsand förrås concentration up to 55% (v / v), för att producrats salts the salt salts of inducing a minced tryck 225 mbar el-15 ler mindre och ätervinns genome att condenser, kanknetecknat av att Bade bland-Ning, indunstning och sedimentation av laksulfatmonohydrat utförs i samma en-staka Kari. 12. Förfarande enligt nagot av patentkraven 1-10, kännetecknat av att det so förfarandet utförs som en diskontinuerlig process.